>>24534167 (OP)No-one has heard of Peter Cheyney now but he was the top-selling English author for a period during the 1930s/40s, I believe. He wrote hard-boiled detective or spy thrillers.
He had several recurring characters. This is the series featuring a London P. I. called Callaghan:—
The Urgent Hangman (1938)
Dangerous Curves (1939)
You Can't Keep the Change (1940)
It Couldn't Matter Less (1941)
Sorry You've Been Troubled (1942)
They Never Say When (1944)
Uneasy Terms (1946)
(Plus one or two collections of short stories.)
You Can't Keep The Change and They Never Say When probably have the trickiest plots, as I recall, but it's really best to go in order. If you don't like The Urgent Hangman you won't like any of them.